For certain diseases which are localized to a particular part of the body, the systemic administration of drugs for the treatment of these diseases is not preferred because of the inefficiencies associated with the indirect delivery of the drugs to the afflicted area. Also, if a drug causes significant side effects, it is generally inappropriate for systemic delivery.
Instead, it is preferred that the drug be directly applied to the diseased tissue. Because such localized delivery to the afflicted area usually requires a relatively small amount of drug, side effects of the drug are reduced. Also, since localized delivery requires smaller amounts of drugs, such delivery is desirable for expensive drugs.
However, such localized delivery of drugs to the walls of lumens, such as blood vessels and ducts, can be problematic since body lumens are generally involved in the transport of body fluids, which tend to carry the drug away from the afflicted area. Thus, there is a need for devices and methods for the localized delivery of drugs to afflicted tissue, especially body lumens.
Also, if a drug or biologically active agent is biologically derived (e.g., a gene, a protein or a lipid), it usually cannot withstand standard sterilization of the device (e.g., ETO, gamma, or e-beam sterilization, autoclaving). Thus, the number of drugs that can be incorporated into the implantable device is limited. Hence, there is a need for a method for including such drugs into a drug-releasing device.
A number of methods for delivering drugs to body lumens or vessels involve the use of catheters having expandable portions, such as a balloon, disposed on the catheter. For instance, U.S. Pat. No. 5,304,121 to Sahatjian, PCT application WO 95/03083 to Sahatjian et al. and U.S. Pat. No. 5,120,322 to Davis et al. describe medical devices in which the exterior surface of the device is coated with a swellable hydrogel polymer. A solution of a drug to be delivered to the afflicted tissue is incorporated into the hydrogel. The drug is usually pre-sterilized by such methods as filtration. The drug is held within the matrix of the hydrogel. In the case where the medical device is a balloon catheter, the drug is delivered by inserting the catheter into the body lumen and expanding the coated balloon against the afflicted tissue of the lumen to force the drug from the hydrogel into the tissue.
However, these hydrogel coated devices have certain disadvantages. In particular, because the loading of the drug into the hydrogel is based on diffusion, the amount of drug that can be loaded onto the devices is limited. Thus, there remains a need for a way to load more drug onto implantable devices.
Other methods for making a drug coated implantable device include ones in which a composition of a drug, a polymeric material and a solvent is applied to at least a surface of the device. Such a method is described in co-pending application Ser. No. 08/633,490, filed Jun. 13, 1996 and published as EP 0 822 788A2 on Feb. 11, 1998. Also, U.S. Pat. No. 5,464,650 to Berg et al. describes drug containing coatings for medical devices.